If you use Raspberry Pi, please note the following with the 3.4.x releases:

With the 2D refactor, running in pure software mode simply is not playable on the Pi, anymore. However it will continue to be supported because running it on the VideoCore4 GPU chipset works, for now. Please note that Pi boards that are revisioned 2 or 3 are the only ones currently supported - you can run GZDoom on a Pi 1 but you must make some compile tweaks and it is not officially supported right now. (In other words - you're on your own!)

I should mention that none of this is officially supported by the Raspberry Pi Foundation as of yet - as is repeatedly said, "do this at your own risk" - the drivers for VC4 are still being perfected as of this writing. No one but you (not me, not the rest of the GZDoom team, not the Raspberry Pi foundation, not your distro's distributor, and not your seller) takes any responsibility, should anything go wrong if you follow these instructions.

To activate it - first, make a backup copy of your /boot/ folder and store it somewhere safe. This contains configuration settings as well as your current firmware.

Then, you must do the following (assuming you have a Debian variant - Raspbian has these tools pre-installed):